The biochemistry and cellular localization of the cholinergic innervation of the lateral geniculate nucleus and visual cortex of the cat will be investigated. A tissue slice preparation will be used to characterize the uptake kinetics and metabolism of choline. Uptake of 3H choline followed by autoradiography under dry conditions will be used for studying cellular localization. The localization of muscarinic and nicotinic cholinergic receptors in the visual system of the cat will be investigated autoradiographically using radiolabelled cholinergic receptor ligands. Prior to the localization study the pharmacology, binding affinity, and number of available sites in various regions will be investigated in homogenates. To attempt to identify other neurotransmitters acting in the visual cortex, including presently unknown neurotransmitters, tissue slices will be prepared from visual cortex, and the compounds that are released from these slices will be characterized. The conditions of release will be varied in a manner intended to mimic synaptic release, including various manipulations that should either enhance or block synaptic release. Both high-pressure liquid chromatography and gas chromatography/mass spectrometry will be used to characterize and structurally identify the compounds released.